1. Field of the Invention
The invention relates to a vibratory compactor such as a “vibratory roller” that may be used, e.g., to compact backfilled trenches after a pipeline is laid or to compact the floor of a trench prior to laying a pipeline and, more particularly, relates to a vibratory compactor of the above-mentioned type and having an exciter assembly including one or more unlubricated gears. The invention additionally relates to a method of operating such a roller.
2. Discussion of the Related Art
Vibratory compactors are used in a variety of ground compaction and ground leveling applications. Most vibratory compactors have plates or rollers that rest on the surface to be compacted and that are excited to vibrate so as to compact and level the worked surface. A common vibratory compactor, and one to which the invention is well-suited, is a vibratory trench roller.
The typical vibratory trench roller includes a chassis supported on the surface to be compacted by one or more rotating drum assemblies. Two drum assemblies are typically provided, each of which supports a respective subframe of the chassis. The subframes may be articulated to one another by a pivot connection. Each of the drum assemblies typically includes a stationary axle housing and a drum that is mounted on the axle housing and that is driven to rotate by a dedicated hydraulic motor. All of the hydraulic motors are supplied with pressurized hydraulic fluid from a pump powered by an internal combustion engine mounted on one of the subframes. In addition, each drum is excited to vibrate by a dedicated exciter assembly that is located within the associated axle housing and that is powered by a hydraulic motor connected to the pump. The exciter assembly typically comprises one or more eccentric masses mounted on a rotatable shaft positioned within the axle housing. The vibratory system in widest use today is composed of two synchronized counter-rotating shafts, each of which bears one or more eccentric weights. The shafts are operationally mated to one another via two intermeshing gears. A first one of the shafts is driven by a hydraulic motor or similar drive, and the other shaft is driven by the first shaft via operation of the intermeshing gears. This arrangement allows the forces produced by each shaft to cancel each other in the horizontal plane, but complement each other in the vertical plane. The resulting force is more effectively transmitted to the ground and also reduces the vibrations transmitted to the rest of the machine. Vibratory trench rollers of this basic type are disclosed, e.g., in U.S. Pat. Nos. 4,732,507 to Artzberger, 5,082,396 to Polacek, and 7,059,802 to Geier et al.
The entire machine is configured to be as narrow as practical so as to permit the machine to fit within a trench whose floor is to be compacted. Machine widths of under 1 meter (3 feet) are common. This width minimization is made possible by, among other things, housing the vibratory exciter and its included exciter assemblies at least in part within the footprint of the drum. However, housing the exciter within the drum makes the vibratory system more difficult to access for routine maintenance.
The exciter assemblies of the typical vibratory roller run at moderately high speeds on the order of 1,500 RPM or higher. They also are subject to relatively high shock and vibration loads, and must operate in hot-weather environments for prolonged periods of time. Lubrication of these exciter assemblies is required to increase bearing life and to prevent gear wear and noise. Grease lubrication cannot be used on the gears because the grease will not stay on the gear teeth at the rated rotational speed. The exciter assemblies therefore are lubricated via an oil bath. That is, the housing in which each exciter assembly is mounted is filled with a lubricating oil to a level that is typically above the bottom of the gears and just touching the bottom of the eccentric weight when the roller is on a horizontal surface. This lightly contacts the oil to provide splash lubrication.
However, referring to FIG. 10, when the vibratory roller is operated on a slope, as is often experienced when compacting trenches, the oil O flows to one side of the exciter housing H. As a result, one of the gears G1 is immersed in the oil more deeply than desired, resulting in aggressive splashing of oil, creating additional friction and heat. The other gear G2 is not immersed in oil at all. Elevated heat reduces the life of the bearings and seals and also beaks down the lubrication properties of the oil. This requires the periodic replacement of the oil to insure proper lubrication. This maintenance is somewhat burdensome, particularly given that lubricant drain and fill ports are relatively inaccessible in compact trench rollers. In addition, some operators tend not to replace the oil at the required frequency, resulting in premature failure of exciter components.
In addition, any system requiring an oil bath is prone to oil leaks. That is particularly true in the case of vibratory rollers in which the severe vibrations resulting from roller operation can lead to rapid degradation of seals and to the loosening of bolts that connect the components of the exciter assembly housing to one another. These leaks can accelerate wear and failure due to under-lubrication and also present an environmental hazard.
The need therefore has arisen to provide a vibratory roller having an exciter assembly that does not require an oil bath, hence negating the need to maintain a designated level of oil in an exciter assembly housing and immunizing the roller from the detrimental effects of operating on a slope.